PROJECT SUMMARY We will use high throughput techniques to produce a set of viral vectors that will allow selective expression of transgenes in specific populations of neurons in the brain. Along with many other applications, this will allow optogenetic control, recording, and genomic modification of targeted neuronal populations without the need for production of transgenic or knock-out lines. This will provide neuroscience with a versatile and powerful set of tools that will make possible a broad set of new experimental designs that are likely to yield major insights into the organization of neuronal circuits and the biological bases of normal cognition and behavior and the dysfunctions underlying neurological and mental disorders. Additionally, because the new tools are also designed to work in humans, they are likely to result in important new therapies for mental and neurological diseases.